Adding coupon to my forms

I am also looking for answer for this question. please inform me if any one should know about how to add coupon code in the payment form.

It seems that you don't have a form yet. If you have a payment field, you just need to click the "wand" icon to open the payment wizard. Just make sure that the APIs and credentials are correct. After entering the products, you'll see the "Other Options" screen. Here you can click the "Coupons" and configure the settings.

I would recommend you checking the complete guide: How-To-Add-Coupon-Code-in-the-Payment-Form

Hope that helps. Thank you.